The overall objective of the proposed research is to investigate the motor control of the abdominal muscles with particular emphasis on neural mechanisms regulating their respiratory functions. The experiments are designed to record and compare abdominal alpha and gamma motoneuron responses to a variety of respiratory and nonrespiratory stimuli. Abdominal motoneuron discharge will be detected by recording neural activity in peripheral nerve filaments. We will determine if abdominal motoneurons exhibit both rhythmic and tonic activity during eupnea and whether their patterns of discharge depend on descending impulses from medullary centers. We will assess the contribution of both vagal and segmental inputs to abdominal motoneurons during pressure breathing (CPAP) or resisted expiration. We will examine how an increase in FICO2, an increase in FIO2, or a decrease in FIO2 affect the discharge of abdominal motoneurons. We will investigate the effect of induced hypotension on the discharge patterns of abdominal alpha and gamma motoneurons. The results of the proposed experiments will indicate how the medullary expiratory center and abdominal motoneurons integrate sensory imput from a variety of receptors.